1. Field of the Invention
The present invention relates to a hammer shank for a piano, which pivotally moves in accordance with key depression, and a method of manufacturing the same.
2. Description of the Related Art
Conventionally, a hammer of a piano, which has a hammer shank, has been disclosed e.g. in Japanese Laid-Open Patent Publication (Kokai) No. 2005-77455. The hammers are provided in association with respective keys, and each of the hammers is pivotally supported by a hammer shank flange (hereinafter simply referred to as “the shank flange”). Each of the hammers includes a long, slender wooden hammer shank and a hammer head fixed to a rear end of the hammer shank. The hammer shank has a front end thereof bifurcated into two left and right arms extending forward in facing and parallel relation to each other. The shank flange is formed by a synthetic resin molded article, and screwed to a hammer shank rail. The shank flange has a rear end thereof formed with an engaging part projecting rearward, and the two arms of the hammer shank are engaged on the opposite sides of the engaging part. Further, a pin is horizontally passed through the two arms and the engaging part. This pin is rigidly secured to the engaging part, but is supported by the two arms in a pivotally movable manner. Thus, the hammer is pivotally supported by the shank flange via the pin integral with the shank flange. The opposite side surfaces of the engaging part of the shank flange are formed parallel to each other, and each of the side surfaces of the engaging part of the shank flange is opposed to the inner side surface of an associated arm of the hammer shank with a slight clearance.
With the above-mentioned arrangement, as an associated key is depressed, an associated action operates to push up the hammer shank, whereby the hammer pivotally moves upward, and the hammer head strikes an associated string to thereby generate a piano tone. During the pivotal motion of the hammer, the hammer shank is guided by the two arms and the engaging part of the shank flange, so that the hammer can perform the pivotal motion without deflecting laterally.
However, the hammer shank, which is made of wood, is susceptible to a use environment of the piano, particularly to dryness and wetness, and hence there is a fear that smooth and stable pivotal motion of the hammer cannot be obtained due to a change in the dimension between the two arms. Specifically, when the dimension between the arms of the hammer shank is reduced due to shrinkage caused by dryness (see FIG. 5B), the clearances between the two arms and the engaging part is sometimes lost, which causes a defective operation of the hammer, such as incapability of smooth pivotal motion of the hammer (which will be hereinafter referred to as “a stick”). On the other hand, when the dimension between the arms of the hammer shank is increased due to expansion caused by wetness (see FIG. 5A), the clearances between the two arms and the engaging part become larger. As a result, there is a fear that the hammer deflects laterally or wobbles during pivotal motion, thereby hindering the hammer from properly striking the string.